1. Field of the Invention
The invention relates to a method and an arrangement for generating cyclic pulses.
2. Description of the Related Art
Cyclic pulses are needed in many technical fields, such as ultra wide band technology (UWB). A cyclic pulse has both positive and negative amplitudes and can be a bipolar pulse, such as a monocycle or a pulse with several cycles. Cyclic pulses can be produced in several ways. A transistor operated in an avalanche mode produces monocyclic pulses, but as the avalanche breakdown does not take place in the same way each time and as it is sensitive to temperature and other environmental changes, the correlation of the pulses tend to be too low. The solution is also sensitive to noise, requiring a high operational-voltage, which prevents its use in portable devices.
Monocyclic pulses can also be generated with the help of transmission lines. In the solution, a unipolar pulse is divided into two transmission lines. The pulses experience different delays while propagating in the transmission lines and the other line also inverses the polarity of the pulse. The pulses of different transmission lines are then combined, resulting in a monocycle. Also this solution has many problems. The solution is sensitive to noise caused by power supplies, external radiation and circuits connected thereto. The solution may also produce even order harmonics which cannot be suppressed and hence cause big problems. Additionally, the transmission lines cannot be implemented on an integrated circuit, which makes it difficult and too large for many applications, such as portable devices.
It is also possible to generate monocyclic pulses by combining two unipolar pulses in a Gilbert multiplier, which multiplies one input unipolar pulse by one and the other unipolar pulse by minus one. The multiplying factors can be changed, depending on the data bit controlling the multiplication. The multiplying factors define the polarity of the pulses to be combined and, hence, by changing the multiplying factors from one to minus one, or vice versa, the phase of the output monocycle can be changed. The operation principle of a Gilbert multiplier is complicated and, thus, susceptible to problems.
It is an object of the invention to provide an improved solution which is simpler and more immune to disturbances. This is achieved by a method for generating cyclic pulses, the method comprising: inputting a first unipolar pulse to one input of a first differential pair; inputting a second unipolar pulse to another input of the first differential pair, the first unipolar pulse and the second unipolar pulse having inversed polarities with respect to each other; delaying the first unipolar pulse and the second unipolar pulse; inputting the first delayed unipolar pulse to one input of a second differential pair; inputting the second delayed unipolar pulse to another input of the second differential pair; and forming a cyclic pulse by combining an output signal relating to the first unipolar pulse of the first differential pair with an output signal relating to the second unipolar pulse of the second differential pair.
The invention also relates to an arrangement for generating cyclic pulses, the arrangement comprising: a first differential pair including an input for a first unipolar pulse, and a second input for a second unipolar pulse, the first unipolar pulse and the second unipolar pulse having inversed polarities with respect to each other; means for delaying the first unipolar pulse and the second unipolar pulse; a second differential pair including an input for the first delayed unipolar pulse, and a second input for the second delayed unipolar pulse; and the arrangement is configured to form a cyclic pulse by combining an output signal relating to the first unipolar pulse of the first differential pair with an output signal relating to the second unipolar pulse of the second differential pair.
Preferred embodiments of the invention are described in the dependent claims.
The method and arrangement of the invention provide several advantages. Since the solution is based on a differential pair it is rather insensitive to many kinds of interferences such as noise from other electronic devices or circuits or harmonic signals. Successive cyclic pulses are also very constant with little variation.